How are you doing that OSM access Wil?
Did you do a similar test of data flow using the OSM web page? Did you use your browser to access OSM? Here is a discussion showing how to access [OpenStreetMap without the Map Component] (https://groups.google.com/g/mitappinventortest/c/gGAeQN3r_fg/m/Dc8PY5HrAwAJ ) using App Inventor . As a comparison Wil, can you test data usage using network using access to OSM like this example? Knowing that might help MIT.
The app using Map caches OSM tiles. It is probably saving them to the app and continues to down load after screen movement as a guess. That does not happen when accessing OSM directly and might be part of the issue.
Not familiar with your data flow tool. It may be monitoring ALL data flow and why you get the response you see. You discuss excessive rates of severel Gb in an hour. It has been a while since I tested data usage. In an hour long test I made some time ago with network on for an hour, the usage was only on the order of Mb's based on my cell Provider records. Not excessive. I can't explain your usage.
Another developer expressed similar behavior with respect to Map tile behavior a year ago. He reported to MIT, see Evan's reply Map component: frequent tile re-load
The Map component uses some of the code in the LocationSensor component. It will poll a location change every 60 seconds so, depending on the Map settings. The issue could be related to that behavior.
Thanks for your example.
--Steve